1. Field of the Invention
The present invention relates to a method and system for the drilling of holes, of defined geometries. More specifically, the present invention relates to a method and system for the drilling of holes, of defined cross sections of holes, by means of complex laser technologies as further described herein.
2. Description of the Related Art
The related art involves In addition to present conditions on the part of the engine such as combustion chamber shape, air movement and nozzle location, the combustion process in diesel and gasoline engines depends on a multitude of injection system parameters. They include the nozzle design and the appurtenant nozzle hole location, the number of holes, the hole length for the atomization of the fuel into the combustion chamber as well as the amount and chronological course of the injection pressure.
An increase in the overall degree of efficiency of the engine and the reduction of raw emission are consequently determined to a large degree by the optimization of the injection systems. A decisive improvement of the combustion process in diesel and gasoline engines can be achieved via these parameters.
In this context, decisive criteria are the reduction of the size of the fuel droplets as well as of the flow loss during the injection process. Smaller nozzle borings in conjunction with greater pressure generally lead to a smaller size of the fuel droplets. The bore diameter and an aerodynamically efficient design of the borings are relevant parameters in this regard.
For years, the injection pressure has been increased and the spray hole has been reduced for the conversion of an optimal fuel mixture preparation. Since this approach favors cavitation phenomena in the spray hole that in an extreme case will damage the nozzle and in any event reduce the flow through of the nozzle due to the existing gas phase, work has been going on even today with various conicities of the spray holes that taper in downstream direction. Moreover, it shows that if a critical hole diameter falls below approximately 100 μm, carbonization phenomena occur in the spray hole that clearly reduce the flow with increasing age of the aggregate. Now the question arises to what extent one can increase the hydraulic degree of efficiency of the nozzles through specific shapes of the spray hole so that the effects of carbonization and cavitation are prevented and the break-up of the jet is intensified to provide a better air feed into the spray, thereby increasing the life span of the nozzles.
The current state of the art is characterized by the fact that the shape of such holes, regardless of whether they are produced through mechanical drilling, eroding, ultrasound or laser processes, is cylindrical or conical with more or less straight walls. But this way it is not possible to create fluidically optimal conditions for the atomization of fluids.
With regard to the laser methods, numerous proposals exist in the patent literature for an improvement of the accuracies, in particular the sphericity, hole shape or the reduction of the negative impact of melting components on the surface quality of the boring as well as for an enlargement of the hole in the direction of injection. The majority of the considerations are purely geometric/optical, coupled with suitable mechanical components.
Since the parameters of a laser beam, in particular its intensity distribution, does not meet the high requirements made of the sphericity, for example of a hole in injection nozzles, there are several optical/mechanical variants to eliminate this problem. In this regard, DE-OS 32 17 226 A 1 proposes rotating the radiation bundle around its own symmetry axis which in DE-OS 197 45 280 A 1 is expanded to three modules that are arranged in front of the focusing lens and that permit varying the point of impact and its inclination on the workpiece. A specific image rotator is described in DE-OS 197 41 09 A 1, for example.
Measures for an improvement of the surface quality of the boring can be found in DE OS 30 07 169 A 1 in which a sufficiently high heating of the work piece during laser processing is supposed to create a uniform molten film, in DE-OS 27 13 904 A 1 where a second laser beam functions as melting beam that is supposed to melt away the burr created during the actual drilling process, or in patent specifications DE 101 40 533 B 4 where a sacrificial layer is supposed to improve the quality of the drilling by means of ultra-short laser impulses.
Patent specification GB 2227 965 addresses the shape of the hole, specifically its widening in the direction of the jet. Here, controlling the beam is proposed with regard to impact angle and distance between the beam and boring axes with the objective of realizing conical holes of varying wall inclinations in as variable a fashion as possible. The more theoretical considerations concerning the intensity profile of the boring beams in patent specification DE 10 2004 014 820 B 4 serve the same objective. The arrangement described in patent specification DE 99 05 571 C 1 also serves to create defined conical hole shapes with a widening in the direction of the jet. The basic idea consists of a synchronous rotation of the polarization direction of the laser beam with a wobbling motion of the beam created by a corresponding mechanism.
Multi-stage processes consisting of a first step, the pre-drilling, and a second step, the creation of the final drill hole shape, serve to effectuate the entire drilling process on the one hand and to increase the precision of the realized hole on the other hand. To this end, a coupling between laser and erosion processes may be used, as described, for example, in EP 0 299 143 A 1 and DE 10 2004 054 587 B3, or two lasers with different beam properties as shown in DE-OS 101 44 088 A 1 may be used. In DE 10 2004 054 587 B3 it is pointed out, among other things, that, based on the state of the art, in the case of small injection holes with diameters of an 80 μm magnitude, approximately 24 holes per nozzle must be drilled in order to reach the required injection volumes per unit of time. In the case of such large numbers of holes, a considerable negative effect on nozzle stability and thus on functional reliability and durability must be expected in addition to increased labor costs. The novel hole shapes in accordance with the invention which are described in detail in the following, provide an essential step forward in the state of the art from this aspect as well since due to the greatly reduced flow resistances in particular of small holes, such large hole numbers may be dispensed with out making increased demands for example on injection pressure.
What is not appreciated by the prior art is that all the proposals enumerated above lack a deliberate consideration of the characteristics of the interaction between laser radiation and material that are coupled with the wave properties of laser radiation, in particular diffraction, in order to achieve fluidically optimal hole shapes. They are limited to cylindrical holes and conic hole shapes with more or less large opening angles.
Accordingly, there is a need for an improved method and system for the creation of hole cross sections by means of which an optimal atomization of fluids can be assured, with the most important area of utilization being the drilling of injection nozzles for combustion engines.